1. Field of the Invention
The present invention relates to rolling roll profile control equipment that controls the roll profile in the axial direction, that is to say the roll diameter distribution, of a rolling roll in the hot rolling or cold rolling of metal materials.
2. Description of the Related Art
As quality controls in hot thin strip rolling and cold thin strip rolling, there is a strip thickness control, which controls the strip thickness in the central part in the width direction of the strip; a strip width control, which controls the strip width to a set value; and a temperature control, which controls the temperature of the strip to the optimum. In addition, there are such controls as a crown control, which controls the strip thickness distribution in the width direction, that is to say the strip profile; and a flatness control, which controls the distribution of extension in the width direction of the strip.
Of these controls, the crown control and flatness control are the roll bending equipment or roll cross equipment installed at the ends in the width direction of a rolling roll (hereafter referred to as "work roll" or "roll"). Roll bending equipment is the equipment that controls the strip profile by bending the roll. Roll cross equipment is equipment that controls the strip profile by crossing upper and lower rolls in the rolling direction and varying the width direction distribution of the roll gap.
The factors that particularly affect strip profile are the rolling load and roll profile. Of these, the roll profile has a great influence because the rolling roll is in direct contact with the strip.
As causes of variation of the roll profile, there are variations of the thermal crown due to the heat received from the strip (i.e., the roll diameter due to thermal expansion), and wear due to contact between the rolling roll and the strip. FIG. 1 (a) shows a roll profile having a thermal crown for the original roll profile. FIG. 1 (b) shows a roll profile that combines the two factors of thermal crown and wear.
FIG. 2 shows the variation over time of the roll profile of the cross-section at arrows A--A of a work roll, in a position shifted somewhat sideways from the center of the axial direction, in the case of having rolled one strip. Here, the thermal crown, shown by dotted curve P, gradually grows with the passage of time, and there is a tendency to saturate. Wear, shown by dotted straight line Q, progresses at a roughly constant rate. Consequently, the roll profile varies as in curve R, which is obtained by combining these two. These tendencies occur and variously deform the roll at each cross-section. Therefore, the profile of the roll in the width direction does not always become a simple curve such as shown in FIG. 1 (a).
FIGS. 3 (a) and (b) show conceptual thermal crown growth in cases of continuous rolling. Of these, 3 (a) shows the case of a short rolling pitch, and 3 (b) that of a long rolling pitch. In each case these are shown by solid lines and dotted lines (the difference between solid lines and dotted lines will be explained below).
In order to control such roll profile variations for wear, such measures as making the roll out of highly wear-resistant material can be taken. Also, as technology for dealing with the thermal crown, for example, the methods reported in the following publications (a), (b) and (c) are known.
(a) There is a method of altering the reduction ratio of the rolling mill to control thermal crown growth, reported in Laid-Open Patent Showa (Tokkoushou) 56--1161 Gazette as "Hot Strip Rolling Method Designed to Rationalise Strip Crown".
(b) There is a method of adjusting the rolling pitch, reported in Laid-Open Patent Showa (Tokkoushou) 60 --5370 Gazette as "Thermal Crown Control Method and Equipment for Hot Strip Finish Rolling".
(c) There is a method of adjusting roll cooling water, reported in Laid-Open Patent Showa (Tokkoushou) 60--5731 Gazette as "Control Method for Strip Crown in Hot Strip Finish Rolling".
Of the above-mentioned prior art techniques, with the method reported in (a) there were cases when the reduction ratios of the various stands of the rolling mill could not always correct for thermal crown control. That is to say, the reduction ratio directly affects the rolling state and product quality, such as rolling load, crown, and tension of the relevant stand, and was used preferentially in the control of these. In actuality, the frequency of its use as a means of thermal crown control was low.
Also, with the method reported in (b), the rolling pitch is determined based on production plans, and is almost always determined by operational reasons such as the avoidance of trouble. In actuality it was hardly ever used as a means of thermal crown control.
On the other hand, the method reported in (c) is currently the most widely used. However, even when the roll is cooled, it is difficult to control the thermal expansion of the roll due to differences in conditions such as rolling pitch, strip temperature, and the flow and temperature of cooling water.
Generally, to reduce the effect of roll thermal crown, there are methods of controlling the growth of the thermal crown and, provided that the roll profile is constant, the effects on strip profile and strip thickness will reduce. Also, because the roll emits the absorbed portion of the heat received from the strip, very large amounts of cooling water are required, and it is difficult to install that type of roll cooling equipment.
Also, as shown in FIG. 2, the thermal crown has the property of saturation and, when rolling is performed at a comparatively short pitch, as shown in FIG. 3 (a), the effect of the thermal crown variation becomes smaller after saturation.
However, as shown in FIG. 3 (b), when the rolling pitch is long, a once-formed thermal crown cools while awaiting rolling, and is likely to return to its original condition before rolling the next strip. In this case, the effect of thermal crown variation on the degree of rolling appears strongly. Furthermore, when the roll temperature is low, the efficiency of heat release from the strip becomes high. This accelerates the temperature drop at the head end of the strip and often has a bad effect on strip thickness accuracy and the like.
Also, in order to measure the roll profile, a special detector was required that detects the roll profile by scanning, either optically or by contact, in the width direction of the roll, even during rolling. On the other hand, because there are limitations such as space for installing this detector, there is also a method of not directly detecting the roll profile but predicting it from other quantities of state (such as, for example, rolling load and rolling speed). However, as mentioned above, roll profile actually has a very complex behavior due to rolling conditions, and thus prediction accuracy is not high.